1. Field of the Invention
The present invention relates to a method of forming embrittled areas inside a wafer for dividing the wafer in which a plurality of devices is formed.
2. Descriptions of Related Art
Conventionally, a wafer in which a plurality of devices such as IC, LSI and the like is formed is divided into individual devices by a dividing apparatus such as a dicing apparatus, and the individual devices are then used in a variety of electronic devices, such as mobile phones, personal computers, and so forth.
As a technology for dividing the wafer into individual devices, a technology that directs a laser beam of a wavelength capable of penetrating the wafer onto focal points established inside the wafer and irradiating the wafer so as to form embrittled areas inside the wafer has been proposed (see, for example, JP-A-2002-192370).
However, a thickness in the depth direction of the embrittled areas formed inside the wafer that is obtained with a single laser beam irradiation is approximately 20 μm to 30 μm, and therefore in the case of a thick wafer, i.e., having a thickness of 200 μm-300 μm, (for example, for CCD or for MEMS), the embrittled areas must be formed in multiple layers. For example, after forming embrittled areas in multiple layers inside predetermined division lines in a first direction, embrittled areas are formed in multiple layers inside predetermined division lines in a second direction. However, a problem with this approach is that, formerly formed embrittled areas in the first direction form a wall that disperses the intersecting laser beam to be emitted subsequently in the second direction, as a result. Accordingly, in areas where the embrittled areas intersect, embrittled areas are not formed inside the predetermined division lines in the second direction, and thus the wafer cannot be divided correctly along the predetermined division lines.